It is known in the art that fine emulsions, which are dispersions of one immiscible liquid in another, can be produced by vigorous agitation of the combination of the two liquids. An emulsion is a dispersed system containing at least two immiscible liquid phases. Generally, there are three components to an emulsion, a dispersed phase, a continuous phase (i.e., the dispersion medium) and an emulsifying agent.
The production of such emulsions is important in certain industrial applications, e.g., liquid-liquid extraction operations, where it is necessary to create the highest possible contact area between the two liquids in order to obtain high extraction efficiencies. Such vigorous agitation techniques can produce extremely fine emulsions when the two liquids have similar densities.
Various processes have been used for separating the liquids forming the emulsions from the emulsions, as when the extraction or synthesis operation involving the emulsions is complete. For example, it is known in the art to use decanters for easy, gravity separations. For more difficult separations in which the droplets of the dispersed phase are small, it is necessary to increase the size of the dispersed phase droplets so that they can settle out of the continuous phase within a reasonable time. For this purpose, centrifugal coalescers, electrical coalescers and various bed-type coalescers are usually used. However, of these, only bed-type coalescers are capable of separating liquids with very similar densities.
In order to achieve this increased size of the dispersed droplets, various materials have been used to adsorb, on their surfaces, the dispersed liquid. This allows the smaller particles to more readily settle out of the continuous phase. Various theories have been advanced in order to explain the ability of different packing materials used in bed-type coalescers to promote strong coalescence between droplets of the dispersed phase in order to break fine emulsions. However, none of these theories is considered completely satisfactory.
For example, preferential wetting of the packing material by the dispersed phase is regarded as the controlling factor in some of the theories advanced. Packing materials are generally selected based upon their wettability by the dispersed phase. However, Gudeson in "Coalescence of Petroleum Compounds in Mixed Fibrous Beds", M. S. Thesis, Illinois Institute of Technology, (1965), reported that surface roughness of the packing material may be controlling, since coalescence occurs preferentially at certain fixed points of the packing material which are presumably the result of roughness.
Moreover, Bitten in "Study of Aviation-Fuel Filter/Separators", Final Report No. IITRI-C6088-12, IIT Research Institute, p. 322, Chicago (May, 1969), obtained good separation of water from jet fuel by using Teflon.RTM. fibers which are phobic to both water and jet fuel. Microscopic examination of the Teflon.RTM. fibers demonstrated that the surfaces were, in fact, rough.
Various types of packing materials have been used in bed coalescers, including hydrophilic materials such as fiberglass, glass, ceramics, steel and synthetic polymers (e.g., polyurethanes). Various composite materials have been used for water in oil emulsions, while hydrophobic materials (principally, synthetic polymers, e.g., polypropylene) have been used for oil in water emulsions.
In U.S. Pat. No. 3,919,081, the use of acid-washed activated carbon particles was disclosed for separating hydrocarbons from waste water. Contrary to the conventional practice in the art which is to first contact the coalescing bed with the continuous phase in order to obtain maximum performance, this patent discloses that it is critical to presaturate the activated carbon bed with the hydrocarbons in order to obtain good coalescence.
"Coalescence. Industrial Aspects", Revue de l'Institute Francais du Petrole, XXVII, No. 5, pp. 763-783, (Sept.-Oct. 1972), discloses other methods which have been used to break liquid-liquid emulsions. However, these methods are highly specific for the particular emulsion system with which they are being used. Examples of some of the methods disclosed are refrigeration, heating, agitation, addition of an excess of the dispersed phase and violent agitation, addition of certain materials to chemically destroy or alter the emulsifying agent, addition of a solvent in which both phases are soluble and addition of powdered solids (e.g., graphite powder) to increase the efficiency of decanters for separating some oil in water emulsions.
Although it would appear that the addition of powdered carbon or graphite should be a general way of destabilizing oil in water emulsions, it has been found by the present inventors that the opposite is, in fact, true. Frequently, small graphite or carbon particles adsorb on the surface of the oil droplets, preventing their coalescence and thus stabilizing, rather than breaking the emulsion. Such emulsion stabilization due to the adsorption of finely divided foreign particles on the surface of the dispersed phase droplets is a common industrial problem and frequently the emulsion is pre-filtered in order to remove any such foreign particulates. Therefore, although carbon powder and graphite powder previously have been used to break oil in water emulsions, they are not widely used due to their tendency to produce fines which can stabilize the emulsions.
In the production of alkanesulfonyl chlorides by chloride oxidation of either the corresponding alkanethiol or dialkyl disulfide in aqueous hydrochloric acid, good mixing is necessary to maintain the poorly soluble starting materials and intermediate oxidation products dispersed in the reaction medium. Also, good mixing is important to prevent local excesses of chloride which can lead to side-chain chlorinated products. However, highly stable emulsions of the alkanesulfonyl chloride in the aqueous hydrochloric acid can result which are difficult to separate.
A reliable and effective process for separating highly stable emulsions of alkanesulfonyl chloride in aqueous hydrochloric acid is needed. The present invention provides an improved process to break such emulsions, which is accomplished by passing the emulsion through a coalescing bed of carbon or graphite, by passing the emulsion through a layer of alkanesulfonyl chloride, or by a combination thereof.